A restricted-calorie diet inhibited the development of pre-cancerous growths in a mouse model of skin cancer, reducing the activation of two signaling pathways known to contribute to cancer growth and development, a new study by U.S. researchers has shown.

An obesity-inducing diet, by contrast, activated those pathways, a research team from the University of Texas' Anderson Cancer Center reported at the American Association for Cancer Research annual meeting Monday.

"These results, while tested in a mouse model of skin cancer, are broadly applicable to epithelial cancers in other tissues," said the report's senior author John DiGiovanni.

Cancers of the epithelium -- the tissue that lines the surfaces and cavities of the body's organs -- comprise 80 percent of all cancers.

Calorie restriction and obesity directly affect activation of the cell surface receptors epidermal growth factor (EGFR) and insulin-like growth factor (IGF-1R). These receptors then affect signaling in downstream molecular pathways such as Akt and mTOR.

Calorie restriction or negative energy balance inhibits this signaling, while obesity or positive energy balance enhances signaling through these pathways, leading to cell growth, proliferation and survival.

Dietary energy balance refers to the relationship between caloric intake and energy expenditure. Previous research, both experimental and epidemiological, suggests that chronic positive energy balance, which can lead to obesity, increases the risk of developing a variety of cancers, while negative balance often decreases risk.

"These new findings provide the basis for future translational studies targeting Akt/mTOR pathways through combinations of lifestyle and pharmacologic approaches to prevent and control obesity-related epithelial cancers in humans," DiGiovanni said.

(Agencies via Xinhua News Agency April 15, 2008)